1. Field of the Invention
Embodiments of the present invention generally relate to improving the threshold voltage in a thin film transistor (TFT).
2. Description of the Related Art
Current interest in TFT arrays is particularly high because these devices may be used in liquid crystal active matrix displays (LCDs) of the kind often employed for computer and television flat panels. The LCDs may also contain light emitting diodes (LEDs), such as organic light emitting diodes (OLEDs) for back lighting. The LEDs and OLEDs require TFTs for addressing the activity of the displays.
The current driven through the TFTs (i.e., the on-current) is limited by the channel material (often referred to as the active material, semiconductor material or semiconductor active material) as well as the channel width and length. Additionally, the turn-on voltage is determined by the accumulation of the carrier in the channel area of the semiconductor layer which could change as the shift of the fixed charge in the semiconductor material or the charge trapping in interfaces and the threshold voltage shifts after bias temperature stress or current temperature stress. Current MO-TFTs, such as indium gallium zinc oxide (IGZO), zinc oxide (ZnO) and zinc oxynitride (ZnON) TFT devices, have interface problems which can include mobility problems and offset turn on voltages.
Therefore, there is a need in the art for better control of the threshold voltage of TFTs.